While a spacecraft is in an orbit, the spacecraft may be subject to various external disturbance forces which can produce a moment about the spacecraft's center of mass, causing the spacecraft's attitude to change. This change in the spacecraft's attitude is undesirable in that it can result in the spacecraft's payload not being correctly oriented to a selected location. As such, conventional spacecraft often include attitude control systems which enable the attitude of the spacecraft to be controlled within pre-established deadband limits. Such attitude control systems often operate by employing conventional mechanisms such as, e.g., gyros (e.g., laser gyros) and/or conventional star trackers, to enable spacecraft attitude-related information to be detected for use in controlling the spacecraft's attitude.
The use of such conventional mechanisms for detecting spacecraft attitude-related information has a number of associated drawbacks. By example, conventional gyros that are employed for detecting spacecraft inertial rate information are often expensive. Also, in conventional star trackers, which typically employ a large field of view (e.g., 8.degree..times.8.degree.) telescope having a Charge Coupled Device (CCD), the CCDs and the electronic circuits (e.g., such as those needed for providing clock drive signals and video signal processing) associated with the CCDs tend to be expensive, and the electronic circuits are often complex. Moreover, the performance of such components can become degraded if the components are exposed to solar radiation (the radiation hardness of a typical CCD is limited), and thus appropriate shielding must often be provided for protecting the components from exposure to solar radiation.
In view of these considerations, it can be appreciated that it would be desirable to provide a novel and inexpensive apparatus and technique for enabling spacecraft attitude-related information to be detected, for subsequent use in controlling the spacecraft's attitude, and which overcomes the above-described drawbacks associated with the prior art.